You ask who is John referring to and I ask "what is he referring to"........i.e. the NUMBER of the beast....the NUMBER of a man....these both indicate it isn't a who but a what as in what is it referring to......IMHO.
In my study on the number I found it in
1 Kings 10:14 14 Now the weight of gold that came to Solomon in one year was six hundred threescore and six talents of gold (666).....Solomon's wealth corrupted him....could it be a monetary system?
Revelation 13:16-18
And he causes all, the small and the great, and the rich and the poor, and the free men and the slaves, to be given a mark on their right hand or on their forehead, and he provides that no one will be able to buy or to sell,
except the one who has the mark, either the name of the beast or the number of his name. Here is wisdom Let him who has understanding calculate the number of the beast, for the number is that of a man; and his number is six hundred and sixty-six. (no one can buy or sell without the mark....again it relates to money).
1 Timothy 6:9-10
9Those who want to be rich, however, fall into temptation and become ensnared by many foolish and harmful desires that plunge them into ruin and destruction.
10For the love of money is the root of all kinds of evil. By craving it, some have wandered away from the faith and pierced themselves with many sorrows........(the love of money corrupts and controls mankind in evil ways).
But it is very much linked to the antichrist.....so as for myself I believe the number is representing money...a monetary system. The number of his name....the name of Nero Caesar adding up to 666 in Hebrew cannot apply here in Revelation since it is written in Greek....can it?
I found this to be a good read about the number of the beast.....
Why Is the Number of the Beast 666?
Assessing the Options
The problem is that no clear identification can be made linking 666 with any particular ancient historical name. Attempts have been made to alter spellings and incorporate titles to try to make a multitude of names fit, but nothing conclusive has emerged. Most commonly, the number has been identified with Nero, on the basis of a Hebrew transliteration of the title “Nero Caesar.” However, this option flounders on confusion concerning the exact Hebrew spelling of Caesar, and does not fit the fact that John’s readers were largely Greek-speaking, and that Nero had many titles other than Caesar. Additionally, if John were using gematria, he would have alerted his readers by saying something like, “the number in Hebrew (or Greek) is . . .” as he uses the phrases “in Hebrew” or “in Greek” in 9:11 and 16:16, when he wants to draw the readers’ attention to certain significance.
Unsuccessful attempts have been made to identify the number with other Roman emperors, or combinations of emperors. (More than 100 names were proposed in Britain between 1560 and 1830.) Last century the names of Kaiser and Hitler, among others, have also been calculated to equal 666. All attempts to identify the number with the literal calculation of some individual’s name encounter difficulty because of the metaphorical manner in which language and numbers are used in the book. None of the many proposed solutions using the literal gematria form of calculation is ultimately satisfactory because there are so many names, ancient and modern, which could equal the number. The reason for so many proposals, as one commentator says, is that it is easy to turn a name into a number, but complicated to deduce the right name from a number.